I remember a few months back when Dropbox prompted me to migrate the file. I thought it was done. Alas, doesn't appear so.
There is no directory or file in my ~/Library/ folder called "CloudStorage". How do I initiate the migration to ~/Library/CloudStorage ?
Why am I bringing this up now?
Because Dropbox just gave me a heart attack: in the terminal I had moved an (apparently) online-only file out of Dropbox and into non-Dropbox'd directory...and then found the file was zero bytes because Dropbox on my MacOS hadn't retrieved the file before MacOS copied it. Luckily I was able to restore it using Dropbox Web.
Googling found about the need for the migration...so I'm hoping that the migration will prevent this in the future.
How do I initiate the migration to ~/Library/CloudStorage ?
Dropbox is still rolling out the update to all accounts. The goal is to have the update rolled out all to accounts by the end of May. If you want it early you can enable Early Releases (i.e. beta versions) on your account and wait for a notification that your account is ready for the update.